The most significant problem of a conventional hybrid rocket is its very low fuel regression rate; however, paraffin-based fuels are known to have a much higher regression rate. It was determined by Karabeyoglu et. al. that the materials with low surface tension and melt layer viscosity, such as paraffin-based fuels, generate more entrainment of liquid droplets, resulting in increased regression rates. It was very interesting model for us. Therefore we confirmed it experimentally by observing

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... e burning fuels with a visualization chamber and revealed the high regression rate mechanism of paraffin-based fuels. And then we tried to increase the regression rate moreover with swirled oxidizer flow. It was quite effective, approximately twice of the regression rate of no swirl, but a large amount of liquid fuel was observed in the chamber. It is necessary to vaporize the liquid fuel rapidly to obtain high combustion efficiency. We tried to resolve this problem with a baffle plate set in the combustion chamber and obtained 3% combustion efficiency improvement.